Passive systems are being implemented in several nuclear plants already constructed, under construction or under design. The purpose of these systems is to increase the inherent safety of the plant in any transient condition, so they can provide a higher safety level in case of an accident. Best estimate thermal-hydraulic system codes, widely adopted in the nuclear field to perform deterministic safety analyses, need to be validated against the phenomena typical of passive systems (e.g. natural circulation, thermal-hydraulic behavior of large pools, low pressure phenomena, etc.). An experimental test facility called PERSEO (in-Pool Energy Removal System for Emergency Operation) was built at SIET laboratory in Piacenza (Italy) modifying the existing PANTHERS IC-PCC facility. It is a full-scale test facility aimed at studying a new passive heat removal system and it can be used to analyze the capability of system codes to simulate the related phenomena. In the present analysis, Test 9, which was performed in the PERSEO facility at around 4.1 MPa to study the activation and the heat removal capability of the proposed system, has been simulated with the RELAP5-3D code to assess its capability to predict the dominant phenomena of the transient. Particular attention has been dedicated to the analysis of condensation heat transfer coefficient computed by the code, since in previous analyses it has been found an evident underestimation of the power exchanged by the passive system. Alternative correlations for the condensation heat transfer coefficient have been identified and a correction factor for the heat transfer coefficient calculated by RELAP5-3D has been computed. After the application of the correction factor, the set composed by Nusselt-Kutateladze-Chen correlations provided the better agreement with the experimental data. Finally, the accuracy of the code calculation has been evaluated qualitatively and quantitatively by adopting the Fast Fourier Transform Based Method.

一些已经建成、在建或正在设计的核电站正在实施无源系统。这些系统的目的是提高电厂在任何瞬态条件下的固有安全性，以便在发生事故时提供更高的安全水平。最佳估计热工水力系统代码在核领域广泛用于执行确定性安全分析，需要针对被动系统的典型现象（例如自然循环、大型水池的热工水力行为、低压现象等）进行验证。 ）。在皮亚琴察（意大利）的 SIET 实验室建造了一个名为 PERSEO（用于紧急操作的池内能量去除系统）的实验测试设施，用于修改现有的 PANTHERS IC-PCC 设施。它是一个全面的测试设备，旨在研究一种新的被动散热系统，可用于分析系统代码模拟相关现象的能力。在目前的分析中，测试 9 在 PERSEO 设施中以大约 4.1 MPa 进行以研究所提出系统的激活和散热能力，已使用 RELAP5-3D 代码进行模拟，以评估其预测主导因素的能力。瞬态现象。特别关注由代码计算出的冷凝传热系数的分析，因为在之前的分析中发现被动系统交换的功率明显低估。已经确定了冷凝传热系数的替代相关性，并计算了由 RELAP5-3D 计算的传热系数的修正系数。应用校正因子后，由 Nusselt-Kutateladze-Chen 相关组成的集合与实验数据具有更好的一致性。最后，采用基于快速傅里叶变换的方法对码计算的准确性进行了定性和定量评价。